Traditionally, desktop computers have been provided with two different types of external communication interface, namely peripheral interfaces (such as serial and parallel ports) for connecting local peripheral devices, and network interfaces for providing connectivity to a computer network to which other computers and shared resources are connected. For each type of interface connection, communication between the desktop computer and a connected device is effected according to a predetermined protocol scheme; however, the protocol schemes used for peripheral interfaces have generally been much simpler than for network connectivity. Thus peripheral connection schemes frequently did not have to deal with addressing problems as they provided for connection to one device and even if multiple devices were addressable only a very simple address space was used; in addition, protocol schemes used with peripheral interfaces have generally not been structured in multiple layers. In contrast, network protocols are highly structured and have fully developed adddressing schemes, typically using hardware device addresses of six bytes in length providing for global uniqueness of connected device addresses. Of course, these differences are not surprising due to the very different demands placed on peripheral connections and network connections, the former generally calling for large data transfers to/from local devices with the computer being the system master whereas the latter has in the past involved the transfer of smaller amounts of data often on a global basis with the computer having no pre-eminent position in the overall system.
Modern connection technologies such as Fibre Channel are, in fact, quite capable of supporting both high-speed local peripheral transfers and network connections through a single computer interface. However, the investment required to have a single connection technology serving the needs of a modem office is considerable and it seems likely that users will continue to demand appropriately tailored technologies for their peripheral and network interconnect requirements rather than a single solution that will be unnecessarily performant in some areas. This is particularly so in view of the heavy investment in existing network technologies. In other words, as the cost of upgrading a network to give a level a performance demanded by only some of the connected computers will be many times the cost of providing those computers with high-performance peripheral interconnects, the latter solution will often be the preferred one. It may therefore be expected that desktop computers will continue to need both specific network interfaces for the existing technologies and additional communication interfaces for supporting ever-more demanding local needs. It may also be noted that even though recent years have seen a trend to place expensive resources such as printers onto networks, as the prices of such devices continue to drop and users continue to experience the frustration of a network (or at least the relevant server) "going down" and depriving them of a shared resource, there can be discerned a reverse trend in which individual users are demanding their own local printers directly connected to their computers independently of any external network connection.
Another connectivity issue of increasing importance in recent times is the need of users of portable computers, such as frequent travellers, to exchange data between their portable computer and a desktop computer at their office or home. Traditionally, there are a number of ways this can be achieved. For example, the user could copy data from one computer onto a floppy disc, transfer this disc to the other computer, and then read in the data, always assuming that both computers have compatible floppy disc drives. The foregoing approach is obviously very inconvenient and a much more common approach, illustrated in FIG. 1 of the accompanying drawings, is to interconnect the portable and desktop computers 10, 11 through their serial or parallel ports using a suitable cable 12. Appropriate software running on both computers is then used to effect the desired data transfer. The drawback of this approach is that with current standard serial and parallel port designs, the data transfer rates are low and the mechanics of making the connection are cumbersome (the cables and cable connectors required being relatively substantial and the mating connectors provided on the computers being invariably located in inconvenient positions since for most usages, they are only infrequently accessed).
Another approach to providing inter-connection between a portable and a desktop computer is to use a "docking station" providing a relatively direct connection between the bus systems of the two computers; this generally enhances the data transfer rates achievable but at a significant cost premium in providing the docking station.
A further possibility is to use an infrared link between the two computers as illustrated in FIG. 2; in this case, both the portable computer 10 and the desktop computer 11 are provided with infrared transceivers 14 which when lined up with each other enable an infrared link 15 to be established giving high data transfer rates. This approach has in practice been found to be very sensitive to the correct alignment of the transceivers and cannot currently be considered a robust solution.
Yet another approach is to use a computer network to interconnect the portable and desktop computers. FIG. 3 illustrates one possible arrangement based on a 10BaseT network (see ANSI/IEEE 802.3 standards). In this case, each computer or other DTE (in FIG. 3, portable 10, desktop computers 11) is connected by two UTP (Unshielded Twisted Pair) lines to a corresponding port of a multiport repeater unit 20A, 20B. One UTP line 21 serves to transmit signals from the DTE to the repeater unit and the other UTP line 22 serves to transmit signals from the repeater unit to the DTE. Signals received by the repeater unit at any port are repeated on the outgoing lines of all other ports. FIG. 4 shows another network arrangement suitable for interconnecting a portable to a desktop computer. This arrangement which is described in WO-94/13072 (Farallon Computing) is also based around 10baseT network technology but now the repeater unit is effectively distributed over the network between a series of auto-crossover transceivers 25 in a way that allows daisy-chaining of the DTEs (in this case, computers 10 and 11A,B,C). Each transceiver is associated with a DTE and receives power from it when the DTE is switched on. When energised, the transceiver operates as a three port repeater, both transferring signals along the daisy-chain of transceivers and exchanging signals with its associated DTE over cable 27 that typically connects to the serial port of the DTE. Each transceiver includes bypass relays which maintain the daisy chain when the corresponding DTE is turned off resulting in de-energisation of the repeater circuitry of the transceiver. The transceiver 25 can be implemented either as a separate unit (as illustrated in FIG. 4 for computers 11A and 11C), or as a card insertable in a desktop computer (as for computer 11B). In FIG. 4, the portable computer 10 is shown attached at the end of the daisy chain, depending from the repeater 25 associated with computer 11A.
An advantage of providing inter-connectivity between a portable computer and a desktop computer by means of a network is that the same connection to the portable also enables the portable computer to communicate with the other devices connected to the network; if portable/desktop connectivity is provided through a peripheral interface to the desktop computer then, of course, a second connection would need to be made to the portable to establish a network connection. However, many of the existing installed network technologies are really only suited for network traffic profiles and do not cope efficiently with high speed, high volume data transfers. As already discussed above, it is unlikely that there will be a rapid chageover to more performant network technologies so that to achieve high performance in data transfers between a portable computer and a dektop computer, the most generally useful solution will be one using a specialised connection rather than a standard network connection.
Nevertheless, it is clear that from a user perspective, having to make only one connection for both desktop computer and network access is desirable. A further desirable feature so far as a portable-computer user is concerned would be the ability to make network connectivity to any convenient network regardless of the network technology and without the need to carry around interfaces for each network type.
It is an object of the present invention to provide apparatus having a communications interface satisfying at least some of the connectivity needs described above.